<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <from>
        <select>
            <option>请选择学习内容</option>
            <option>Java</option>
            <option>Web前端</option>
            <option>Python</option>
        </select>
    </from>

    <form>
        <select>
            <optgroup label="学习">
                <option>Java</option>
                <option>Web前端</option>
                <option>Python</option>
            </optgroup>

            <optgroup label="娱乐">
                <option>游戏</option>
                <option>看电影</option>
                <option>旅游</option>
            </optgroup>

            <form>  
                <input type="text">
                <textarea cols="30" rows="10"> 我是一个文本框</textarea>
            </form>
            <form>
                <label for="username">用户名:</label>
                <input type="text" name="username" id="username">
            </form>
        </select>
    </form>
</body>

</html>